Liam Neeson spends just about the entire running time of "Unknown" looking grievously harried. He never cracks a smile, although many bones, his and other people's, are cracked.

He plays Dr. Martin Harris, a biotech scientist newly arrived in Berlin for an international conference with his shiny blond wife, Elizabeth (January Jones). About to check into their swank hotel, he realizes he's left his valuable briefcase back at the airport, hails a cab, is almost killed in a car accident, and spends the next four days hospitalized in a coma. When he comes to, he discovers that his wife doesn't recognize him and another man (Aidan Quinn) has assumed his identity. So who's the crazy one here?

For a movie like this to work, you have to be prepared to overlook a plethora of implausibilities. The more enjoyable the ride, the more forgiving we can be. Hitchcock thrillers were far from airtight, but we were having too much fun to care. With "Unknown," the cat-and-mouse game that the filmmakers are playing with us is only partially successful because this thriller is only intermittently thrilling. Instead of being captivated by the twist and turns, we're more likely to be rankled.

Directed by Jaume Collet-Serra and written by Oliver Butcher and Stephen Cornwall, the film also suffers in comparison to the "Bourne" films, which also had an amnesiac as its hero. I'm not a big fan of the "Bourne" movies but at least they hung together better than "Unknown" (which, by the way, was originally titled "Unknown White Male" before wiser heads prevailed).

For all the film's reality games, the best sequences are decidedly unfancy. Collet-Serra stages a couple of above-average car chase scenes – he's particularly good with skidding U-turns – and there's a cloak-and-dagger sequence in a high-end photo gallery that, although it could have been defter, carries a Hitchcock vibe.

A few supporting players liven things up. As the cabdriver, a Serbian illegal immigrant who was speeding Martin to the airport, Diane Kruger is a one-woman rescue squad. She manages to be both winning and winsome, although never enough to bring a smile to Mr. Grumpypuss. Bruno Ganz shows up for a terrific cameo as a former STASI agent and steals whatever there is to steal in this movie. Frank Langella, upping the bad guy quotient with his smooth menace, puts in a welcome appearance near the end.

"Unknown" is framed as a cautionary thriller about the perils of high-stakes terrorism, but I took away a different message from it: Don't forget your briefcase at the airport. Grade: C+ (Rated PG-13 for some intense sequences of violence and action, and brief sexual content.)